Transdermal and topical drug delivery can be used for therapeutic treatment, but the number of molecules that can be effectively delivered using these routes can be limited by the barrier properties of skin.
A number of different skin treatment methods have been proposed in order to increase the permeability or porosity of the outermost skin layers, such as the stratum corneum, thus enhancing drug delivery through or into those layers. The stratum corneum is a complex structure of compact keratinized cell remnants separated by lipid domains. The stratum corneum is formed of keratinocytes, which comprise the majority of epidermal cells, that lose their nuclei and become corneocytes. These dead cells comprise the stratum corneum, which has a thickness of only about 10-30 microns and protects the body from invasion by exogenous substances and the outward migration of endogenous fluids and dissolved molecules. Various skin treatment methods include the use of microneedles, laser ablation, RF ablation, heat ablation, sonophoresis, iontophoresis, or a combination thereof.
In some cases, these treatments are provided by a single integrated device that performs two separate functions: the device treats the skin and also delivers an active ingredient to the treated skin. An example would be a hollow microneedle array with an attached drug reservoir. The microneedles pierce the skin and remain attached while the drug flows from the reservoir into the skin. Although devices of this type may be conceptually easy for a patient to administer, they can be complex and/or limited in the amount of drug they can effectively deliver.